Cathode ray device



Nov. 20, 1962 E. ATTI 3,065,375

cATHoDE RAY DEVICE 22 2O ,8x F'lled July 14, 1958 '8 Fig. I

77 Flg. 6 '6 f F: 26 W /76 7h80'- F Ig. 7

I,'22 S. F |60 l|22 r|20 l 47 i Y l 4g lw55 5 |20 u U U ,26h12 |26 UniteStats This invention relates to electron devices and more `specificallyto those of the cathode ray tube type 1n which use is made of anintensity modulated electron beam. In these devices, an electron gun isnormally provided to generate and form an electron beam of smallcross-sectional area.

One particular application of the cathode ray tube is within thetelevision industry, in which, the electron gun is utilized within thecathode ray tube to generate an electron beam of small cross-sectionalarea. This beam is scanned across an electron sensitive screen whichemits light in response to the electron bombardment and thereby displaysa light image corresponding to the intensity modulation on the electronbeam. Various types of electron guns have been employed in the picturetube industry and one particular structure which is representative ofthe common type gun structure is in United States Patent No. 2,773,212,entitled Electron Gun by I. H. Hall, issued December 4, 1956, andassigned to the same assignee.

The conventional electron gun utilized in television display tubes isconstituted basically of two axially ar' ranged systems. These twosystems are the beam forming, and modulation system and the principallens system. The purpose of the beam forming and modulation system is toprovide a well dened electron beam of controlled intensity to theprincipal or main lens. The principal lens provides the necessaryfocusing of the electron beam emitted from the beamforming andmodulating system to a small spot on the viewing screen. The principallens of the electron gun is usually of the electrostatic or elec--tromagnetic type. Most electron guns including the ones presently usedin the television industry possess a beam forming and modulating systemwhich comprehends a lens known as an immersion lens. This invention isdirected primarily to the beam forming and modulating system of theelectron gun and the description and drawings will refer princip-ally tothis portion of the gun.

In the present type of television display systems, the electron beam inthe cathode ray tube must be amplitude modulated within wide limits inorder to reproduce the desired picture high lights, low lights, and allintermediate values of brightness for adequate picture presentation. Forexample, in a direct viewing tube the electron beam may reach peakvalues of currents as high as 1500 microamperes in the high lightportion of the picture and must go as low as zero microamperes for beamcutoff in the black regions. To modulate the electron beam throughoutthis large current range, it is required that a relatively large pictureor video signal be applied to the gun to modulate the intensity of theelectron beam. A typical amplitude of video voltage required to drivethe elcetron beam from zero up to 1500 microamperes is about 60 volts inthe modern television tube. This large amount of drive that is requiredis primarily due to the low transconductance of the present electron gunstructure.

In conventional television receivers, the video detector supplies asignal which is normally less than 5 volts peakto-peak. Due to this lowvalue, the signal cannot be utilized to directly drive the presentcathode ray tubes. It is necessary that the video signal from thedetector be amplified to a much higher level of the order of 25 times.

3,065,375 Patented Nov. 20, 1962 This requires that the video amplifierbe capable of providing a relatively large gain throughout the entire3.5 megacycles per second bandwidth of the conventional picture signal.It is, therefore, necessary that the video amplifier be a relativelyhigh power and expensive device because of the high output drive voltageand the large total shunt capacitance associated with the picture tubedrive circuit. This capacitance is primarily made up of the outputcapacitance of the video amplifier tube, the input capacitance of thecathode ray tube and the additional capacitance due to wiring socketsand other components associated with the picture tube drive circuit.

The primary limitation in reducing the video drive of the presentcathode ray tube is that due to the extremely stringent electron opticalrequirements which must be met by the electron gun in order to producesharp and bright pictures. Due to the limitation of presently availableelectron optical lenses, only an extremely small area of the electronemissive coating of the cathode can be utilized for the formation of theelectron beam. The high resolution requirement and the high brightnessare mutually coniiicting in that the size of the spot increases withincreasing beam current. The industry has attempted in many ways tosolve this problem, but at this time little success has been had inreducing the drive requirements of the cathode ray tube.

The applicant in his copending application entitled An Electron Device,Serial No. 705,583, liled December 27, 1957, and assigned to the sameassignee, discloses a device in which an electron optical section of theelectron gun is designed to meet the resolution and brightnessrequirements and a transconductance section is designed to meet thedrive requirements. The two sections are entirely separated in function.The structure described in the copending application is of the screengrid type of electron gun.

This invention is directed to a modification of the copendingapplication which provides a structure which may be utilized either witha screen grid type of electron gun or any other type of electron gunregardless of whether a screen grid is utilized. In the structuredescribed herein, the final anode of the transconductance section whichbasically provides a video amplifier sectionl operates at a potentialentirely distinct from the potential applied to the first acceleratoranode of the electron gun itself. This is accomplished in this inventionbecause the control grid of the electron gun is utilized to perform themultiple function of the intensity control of the electron beam and alsothe anode of the amplier or transconductance section of the electrongun. The structure described herein may be operated with a positivegoing or black positive signal applied to the control grid of theamplifying section of the cathode ray tube. A black positive signal isone which causes negative variations of the electron beam current bymeans of positive Variations of the video signal. Thus black or cut olis achieved when the video component of the signal reaches its peakpositive value. y

lt is accordingly an object of this invention to provide a hightransconductancc wideband cathode ray gun.

It is another object to provide an improved high transconductancewideband electron gun structure which offers maximum flexibility ofdesign to achieve the highest performance capabilities in relation tothe operational requirements imposed on the electron gun.

IIt is another object to provide an improved high transconductancewideband television gun structure which provides a favorable transfercharacteristic for better tonal rendition of the reproduced images.

It is another object of this invention to provide a hightransconductance Wideband electron gun in which the direct currentcomponent contained in the input signal is preserved in the modulatedcathode ray beam.

lt is another object to provide an electron beam modulation system whichprovides amplification of the video signal applied which may be adaptedto be utilized in any electron gun structure.

These and other objects are effected by my invention as 4will beapparent from the following description taken in accordance with theaccompanying drawing, throughout which like reference charactersindicate like parts and in which:

FIGURE l is a View of a cathode ray tube partly in section embodying theprinciples of my invention;

FIG. 2 is an enlarged sectional View of a portion of the electron gunstructure illustrated in FlG. 1;

FIG. 3 is an operational View of a portion of the electron gun structureshown in FIG. l to explain the operation of the invention;

FIG. 4 illustrates a modification of the operational View illustrated inFIG. 3;

FIG. 5 illustrates another operational View which is a modification ofthe electron gun structure shown in FIG. l;

FIG. 6 is a top sectional view of a modification of the structure shownin FIG. 2; and

FIG. 7 is a side view, partly in section, of the View shown in FIG. 6.

Referring in detail to FIG. 1, there is shown a cathode ray tubeembodying my invention. The tube is comprised of an envelope 12 having atubular neck portion 14, a ared bulb portion 16 and a face plate portion18. The face plate or viewing portion 18 of the envelope 12 has asuitable fluorescent coating 20 of a phosphor material deposited on theinner surface of the face plate 18 and may have an electron permeableelectrically conductive coating 22 deposited on the exposed surface ofthe phosphor coating 2) as illustrated in FIG. 1. The flared portion 16of the envelope 12 is provided with an electrically conductive coating24 of a suitable material such as carbon or aluminum which extends intothe neck portion 14 of the envelope 12.

An electron gun 30 is mounted within the neck portion 14 of the envelope12. The gun 30 consists essentially of a beam forming and modulatingsystem and a principal focusing electron lens electrode system. Theconducting coating 24 on the interior surface of the flared bulb portion16 serves as an anode of the cathode ray tube and is provided with asuitable voltage supplied by means of an exterior terminal 25. Theelectron gun described and shown in FIG. 1 is of the electrostatic focustype. There is a suitablel deection system provided for dellecting theelectron beam to scan a raster on the screen 20. In the specificembodiment shown, `the deflection system is illustrated as anelectromagnetic deflection yoke 28.

The modulating system of the electron gun 30 in FIG. l is illustrated inmore detail in FIG. 2, and in the operational view shown in FIG. 3. Themodulating system illustrated in FIG. 2 consists of a modulating grid 40which is formed in the shape of a cup member with the open portionfacing to the rear with respect to the screen 2G of the cathode raytube. A spacer member 42 of a suitable insulating material such as micaor ceramic is mounted to the edge of the cup-shaped member 40 bysuitable means. A centrally located aperture 44 is provided in thebottom portion of the cup-shaped member 40. The cup-shaped modulatinggrid 40 is of an electrically conducting material. The spacer `42 isprovided with apertures through which extensions 41 provided on the edgeof the cup-shaped member 40 are inserted. The extensions 41 may bedeformed in a wellknown manner in order to lock the spacer 42 securelyto the modulating grid 40.

An indirectly heated cathode 46 is provided for supplying the necessaryelectron emission for the electron beam of the gun structure and ispositioned within the cupshaped modulator grid 44. `In the specificembodiment shown, the cathode 46 is comprised of a tubular member 48 ofelectrically conductive material which is coaxially positioned withinthe modulator grid 4()` and of a shorter length than the depth of thecup-shaped grid 40. The end of the tubular member 48 adjacent the bottomof the cup-shaped grid 40 is closed with an electrically conductivemember 47 and an electron emissive coating 49 is provided on theexterior surface of this closed end portion 47. The electron emissivecoating 49 is provided adjacent to the aperture `44 in the bottom of thecupshaped grid 44 and is of a greater area than the aperture 44 andclosely spaced thereto. The beam forming cathode 46 may be supportedwithin the cup-shaped grid member 40 in any well-known manner and in thespecific embodiment shown is retained by support member 5G attached tothe outer surface of the tubular member 48 with the other end of thesupport member 50 anchored within apertures provided Within the spacerelement 42.

The amplifying section of this modulating structure is positioned on theopposite side of the spacer 42 with respect to the modulator grid 44.The amplifying section is mounted on the spacer 42 and consists of acathode 52 which is comprised of a tubular member S4 of electricallyconducting material of similar diameter as the tubular member 48. Thetwo members 54 and 48 are coaxially positioned and will be locatedsubstantially on the axis of the electron gun 30. One end of the tubularmember 54 is mounted within an aperture provided in the spacer element42 and a spacer element 55 of similar material as element 42' is alsoprovided at the opposite end of the tubular member 54. The spacerelement 55 is also provided with a centrally located aperture throughwhich the tubular member 54 passes yand is positioned thereby. Anelectron emissive coating 56 of suitable material is provided on theexterior surface of the tubular member 54 between the two spacerelements 42 and 55. A heater element 5S is provided in the tubularmember 54 and extends into the tubular member 48 which is a part of thebeam forming cathode 46 so as to provide the necessary heat for bothcathodes. The heater 58 provides the necessary energy to excite electronemission from the electron emissive coatings 49 and 56. A tubularcontrol grid 60 consisting of a plurality of parallel elements or of amesh structure of electrically conductive material is positioned so asto surround the cathode 52 of the amplifier section. The control grid 60is supported at its ends by the two spacer elements 42 and 55. It may bedesirable to use more than one grid member. An anode or interceptingelectrode 62 is positioned so as to surround both the cathode 52 and thecontrol grid 60 and to intercept the electrons emitting the cathode 52after passing through the control grid 60. The anode 62 is also tubularin shape and is supported at opposite ends by the spacer elements 42 and55. The anode 62 is of an electrically conductive material and ofsuitable strength to securely lock the amplifying section to the spacerelement 42 which is also common to the beam forming and modulatingsection. An electrical connection is made by a suitable conductor 64between the amplifying anode 62 and the modulator grid 40. The techniqueof assembling the amplifying section is similar to that utilized in thereceiving tube art.

Referring to FIGS. l and 3, a screen grid 70 is provided between themodulating grid 40 and the screen 20 of the cathode ray tube. The screengrid 70 is of conventional design and consists of a cup-shaped memberhaving its open end toward the screen 20 andthe bottom portion adjacentthe modulating grid 40. A centrally located aperture 72 is provided inthe bottom portion of the screen grid and is aligned with the aperture44 in the modulating grid 40.

The principal focusing electrode lens system illustrated here consistsof a first anode 'I6 adjacent the screen grid 70 comprised of a tubularor skirt member and a second anode 80 also a tubular member spaced alongthe axis of the tube from the rst anode 76. The end of the skirt portionof the first anode 76 nearest the screen 20 is closed by a diaphragmtransverse and substantially perpendicular to the axis of the tube. Thediaphragm is provided with a centrally locate-d aperture. The end of thesecond anode 80 which faces the lirst anode 76 is also provided with adiaphragm having a centrally located aperture therein. In the specificembodiment shown, the facing ends of the first and second anode have areduced portion. Means in the form of contact members 77 are provided onthe end of the second anode 80 nearest the screen for making electricalcontact to the coating 24 and also to assist in positioning the electrongun 30 within the tube neck 14. The first and second anodes 76 and 80are connected together electrically and are supplied with voltage fromthe coating 24. A sleeve or focusing electrode 84 also tubular with alarger diameter than the first and second anodes 76 and 80 surrounds thespace between the first and second anodes 76 and 80 and is coaxial withthe anodes. The pricipal focusing electrode system comprised of theelectrodes 76, 80 and S4 is of a conventional univoltage type structureand is only an example of a suitable principal focusing lens system.

The electrodes 40, 70, 76, 80 and 84 of the electron gun structure arenormally spaced by providing radially projecting anchor pins 90 from theelectrodes with the pins embedded in longitudinal support glass rods 92as illustrated in FIG. l.

Referring in detail to FIG. 3 which is an operational showing of thestructure shown in FIG. 1, the second anode 76 is normally operated at apotential of about 15,000 volts and a suitable source of potential isillustrated by the battery 100 which has its positive terminal connectedto the anode 76 and the negative terminal connected to ground. It shouldbe remembered that the screen 20 which is collector or anode of theelectron beam is operating at the same potential as the second anode 76.The screen grid 70 is connected to a terminal 101 on the battery 100 toprovide the necessary screen grid voltage which may be, for instance, ofabout 300 volts positive with respect to ground. The modulator grid 40is connected through a load resistor 102 and an inductance 104 to aterminal 103 on thebattery 100 which provides a positive potential lowerthan the one applied to screen grid 70 of about 100 volts positive withrespect to ground. The beam forming cathode 46 is also connected to aterminal 105 on the battery 100 such that its potential, positive withrespect to ground, may be made arbitrarily larger than the potentialapplied to the modulator grid 40 of the amount required to cut the beamoff. This voltage may be about 60 volts.

The cathode 52 of the amplifying section is connected to ground and thecontrol grid 60 of the amplifying section is connected to a video source108. A suitable biasing source illustrated as a battery 110 may also beprovided. The anode 62 is at the same potential as the modulator grid40. The potential difference between the modulator grid 40 and theamplifier cathode 52 is amplitude modulated in accordance With the inputvideo signal applied to the control grid 60 of the amplifying section.This is accomplished by means of the load impedance 102 which isinserted into the circuit of the modulator grid 40. The electron opticalsystem of the gun has both the beam forming cathode 46, the screen grid70 and the anode 76 in FIG. 5 at fixed potentials. The beam modulationwithin the beam forming portion of the gun occurs by natural grid drive.

In FIG. 4, the screen grid 70 and the modulator grid 40 lof the beamforming section are coupled together by a resistor 112 to achieve thecombined actions of both grids 40 and 70 in modulating the electronbeam. The modulator grid 40 in this structure is driving the screen grid70. It also can be appreciated that the coupling resistor 112 may bereplaced by a coupling capacitor.

Brightness control may be obtained by varying the potential of the beamforming cathode 46 from the battery 100. Gain control within theamplifying section may be obtained by varying the value of a resistor114 connected to the amplifying cathode S2 as is illustrated' in FIG. 4.Gain control may also be obtained by varying the bias applied to thecontrol grid 60 of the amplifying section.

With a black positive signal, `it can be seen that the sync pulsescontained in the composite video signal supplied by the video detectorsource 108 to the control grid 62 represent the maximum positive valueof said composite video signal and therefore that the current in theamplifying section is at its peak value during the sync pulses. Thevoltage of the modulator grid 40 will be at its minimum value during thesync pulses. The potential difference between modulator grid 40 and thebeam cathode 46 will be at its maximum negative value so that the beamcurrent is at a minimum value or cutoi During the video portion of theinput signal from the video detector source 108, the signal will be lesspositive and the current within the amplifying section Will decrease.The voltage difference between the beam forming cathode 46 and themodulator grid 40 will become less negative with the result that thebeam current in the electron gun will start flowing and increase fromzero to a value determined by the input signal.

lT he peak level of said beam current will be obtained in correspondenceof the minimum level of the input signal. By taking advantage of thecurvature of the transfer characteristic of the amplifier section, it ispossible to vary within broad limits the gamma of the elec tron gun.

In FIGS. 6 and 7, a modified structure is illustrated. In thisstructure, the cathode-s are positioned transverse to the electron beam.The modulator grid comprises a tubular structure having an aperture 122centrally located in one side thereof. The tubular modulator grid 120 issupported between two spacer members 126 and 128 positioned at oppositeends of the tubular grid 120. Positioned Within the tubular modulatorgrid 120 are the cathode members 130 and 132. The cathode membersconsist of two half sections of a tubular member which are insulatedfrom each other. The cathode 130 is provided with an electron emissivecoating 131 on one surface near the aperture 122 in the grid 120 andsupplies the electron emission for the beam forming structure. The otherhalf section is the amplifier cathode 132 which has an electron emissivecoating 133 which provides the electron emission for the amplifyingsection of the structure. A common heater 136 may be utilized to heatboth the beam `forming cathode 130 and the amplifying cathode 132. Thecontrol grid 13-8 for the amplifier may be a frame like structurepositioned adjacent the amplifying cathode 132 and also supported by thespaced elements 126 and 128. The modulator grid 120 also serves the dualfunction of also being anode of the amplifying section. In the specificembodiment shown, the re-entrant portion 140 is the active area of theanode or intercepting electrode. The first anode 76 of the principallens is adjacent the modulator grid 120 and the screen grid 70 in FIG. lis omitted. This type of gun lends itself to structures possessing Verylow shunt capacitance which is a highly desirable feature particularlywhenever large bandwidths are involved.

While I have described my invention in only a few forms, it will beobvious to those skilled in theA art that it is not so limited but issusceptible of various changes and modifications without departing fromthe spirit ane scope thereof.

II claim as my invention:

l. An electron beam forming and modulating electrode system within anevacuated envelope comprising a first and a second electron dischargepath, said first path comprising a first cathode operating at a firstpotential, a dual function electrode operating at a more positivepotential with respect to said rst potential having a first portion forintercepting the electrons emitted from said first cathode, a controlgrid positioned between said rst cathode and said dual functionelectrode for controlling the electron ow in said first discharge path,said second path comprising a second cathode, an anode, and said dualfunction electrode having a second portion adjacent to said secondcathode and having an Iaperture therein, said dual function electrodemodulating and forming an electron beam from the electrons emitted bysaid second cathode, said second cathode operating at -a positivepotential With respect to said rst potential.

2. A high transconductance cathode ray tube comprising an envelope andhaving therein an electron gun structure to provide an electron beamdirected to impinge upon a target member, said electron gun structurecomprising an amplifier including a cathode, an amplifier control gridand a multipurpose anode electrode, said electron gun also including anelectrode assembly having an electron beam source, a control gridadjacent said electron beam source or controlling said electron beam,said multipurpose electrode being formed to p-rovide the anode for saidamplifier and said control grid for said electrode assembly, saidcathode operating at a potential less than the potential applied to saidelectron beam source.

3. A high transeonductance cathode ray tube comprising an envelope andhaving therein an electron gun structure to provide an electron beamdirected to impinge upon an image display screen within said envelope,said electron gun structure comprising an amplifier including a cathode,an amplifier control grid and a collecting elec-V trode, said electrongun structure also including an elec tron beam source, a control grid,and an accelerating anode for accelerating and focusing the electronsWithin said electron beam, said collecting electrode electricallyconnected to said control grid and operating at the same potential assaid control grid by means of a direct current connection, said cathodeoperating at a potential less than the potential applied to saidelectron beam source.

References Cited in the file of this patent UNITED STATES PATENTS2,055,174 Kwartin Sept. 22, 1936 2,163,210 Wienecke June 20, 19392,173,498 Schlesinger Sept. 19, 1939 2,180,957 Hollmann Nov. 21, 19392,449,339 Sziklai c Sept. 14, 1948 2,454,204 Raymond Nov. 16, 1948FOREIGN PATENTS 1,089,337 France Mar. 16, 1955 brui-

